The present invention relates to a display device using a frame rate control (FRC) method to control gradations of pixels, more particularly relates to a display device and a display method of stripe array and delta array pixels alternately displaying a 2n gradation and a (2n+2) gradation so as to display a (2n+1) gradation.
The FRC method employed in for example a liquid crystal display device is a method of expressing gradations which displays different gradations for every frame in order to expressing an intermediate gradation.
FIGS. 1A and 1B are diagrams for explaining the principle of the FRC method. In the FRC method, as shown in FIG. 1A, a 2n gradation (n≧0) is displayed in a first frame (1F) and a (2n+2) gradation is displayed in a second frame (2F). When repeating this for every frame, as shown in FIG. 1B, a (2n+1) gradation can be expressed. However, since the display is substantially driven at 30 Hz as it is irrespective of it being designed to be driven at 60 Hz, the display ends up appearing to flicker.
Therefore, spatial and temporal processing as shown in FIG. 2 is performed to cancel this out. Specifically, when looking at a certain pixel, the same gradation is not displayed at the adjacent pixels.
However, in 1H1FVCOM inverted drive in which an counter electrode performs an inverted operation for every 1H (1 horizontal period) and for every 1F, if constantly driving the display as shown in FIG. 2, when looking at a certain pixel, the polarity (provisionally indicated by + and −) is written as only +(−) polarity at the time of the 2n gradation display and as only − (+) polarity at the time of the (2n+2) gradation display. The optimum VCOM shifts or a DC component is added to the liquid crystal, therefore the phenomenon of burn-in occurs.
Accordingly, as shown in FIG. 3, when looking at one pixel, this can be avoided by switching the spatial modulation pattern for every 2F so that the pattern of the 2n gradation display and the pattern of the (2n+2) gradation display appear equal including the polarity of the signal (see for example Japanese Unexamined Patent Publication (Kokai) No. 7-120725).
As a pixel array to which the FRC method is applied, there are a stripe array and a delta array.
FIGS. 4A and 4B are diagrams of patterns on a display screen in a stripe array in a case of processing data using the same spatial modulation pattern in a stripe array and a delta array. FIGS. 5A and 5B are diagrams of patterns on a display screen in a delta array a case of processing data using the same spatial modulation pattern in a stripe array and a delta array.
In a stripe array, there is no pixel displaying the same gradation as an adjacent pixel. In the case of a delta array, however, the pixels are offset by 1.5 dots for every row, therefore there is always a pixel displaying the same gradation as an adjacent pixel. Particularly, the pattern in the delta array in FIGS. 5A and 5B suffers from vertical noise and lowers the image quality. Further, these phenomena are conspicuous when the pixel pitch is large due to visual characteristics and when the difference of potentials used for the 2n gradation and the (2n+2) gradation is large.